A prestressing anchorage product is designed and certified for a wide variety of applications: use of 13 mm (.5″) and 15 mm (.6″) strands of all grades (1,770 or 1,860 MPa) including galvanised strands or greased sheathed strands. Prestressing units holding as much as 55 strands
YM Series goods are made from tensioning anchor head, wedges, stressing anchorage plate and spiral reinforcement. Wedge: also referred to as grips or jaws, is made by high-class alloy steel 20CrMnTi. There are two kinds, one is called working grips which is with 2 chips; the one is referred to as tool grips which can be with 3 chips.
Anchor head, also called anchor rings or anchor block, is vital a part of bearing the prestressing tension. There are two kinds of anchor head: one is round anchor head which can be made by 45# high-quality carbon construction steel, and the other is flat anchorage that is created by 40Cr steel. And the prestressing Anchor head must be worked with wedges.
Bearing plate is key component, which transfer the burden from anchor head to concrete under anchor. The process of transfer and distribution of stress impact the anti-cracking and load capacity of concrete. Spiral reinforcement, also known as hoop reinforcement, is utilized for distributing the concrete and strengthening tendons.
A typical misconception exists, which leads some to believe that the creation of openings in existing PT slabs is either extremely complex or impossible. Consideration from the correct procedures demonstrates this not to become the case. Post-formed holes in PT slabs will be different in size ranging from the tiniest penetrations, which can be necessary to incorporate suspended services, to much larger openings to enable the addition of lifts or similar installations. In every post-tensioned slabs, the most frequent tendon layouts use a banded design which offers large, regular spaces between tendons which will easily accommodate smaller openings.
Such instances, alterations can be more straightforward compared to other types of construction, as the creation of holes within these areas can be accomplished without affecting structural performance. The post tension anchorage, in its Guidance Note, identifies four types of post-formed penetration which are categorised based on the effect the operation may have on structural integrity. The initial of those pertains to the tiniest holes, not more than 20mm in diameter, involving no tendon cutting and that offers minimal risk to the structural integrity of the slab. The 2nd group is classed as being a low risk to structural integrity and includes somewhat larger openings, approximately 200mm in diameter in beams or near columns, but larger in areas which can be less stressed.
The voids continue to be located between tendons to avoid the need to cut these. In the third and fourth categories of penetrations, where it will become required to sever the tendons, the effect on the integrity from the structure is likely to be more significant and calls for strengthening and temporary propping from the slab. As the amount of cut traditional reinforcement is significantly less, so is the requirement of corrosion protection to exposed cut steel.
The most typical kind of post-tensioning in the UK marketplace is bonded PT (Figure 4). Ducts carrying high-tensile steel strands are full of grout right after the tendons happen to be stressed and locked off by way of split wedges inside the anchors, thereby bonding the tendons to the concrete. If larger openings are essential in slab steel anchor, they is often treated in a similar manner as traditional reinforced concrete slabs because the results of cutting by way of a bonded tendon remain localised and the rwkhni redevelops its bond both sides in the cut, typically within 1m.
In instances where it really is required to cut multiple tendons, mechanical or epoxy anchorages can be put on the ends of the severed tendons to provide even more security. CCL recently undertook an application that required the creation of voids within bonded slabs, to be able to house a number of hoists as well as an escalator within an existing building. After non-destructively choosing the tendons that spanned with the proposed void within the slab, by means of the ‘as built’ drawings through the operations and maintenance manual, the posttensioning duct was opened (Figure 5) and epoxy grout anchors were then installed around the exposed strand prior to cutting, thereby giving enhanced surety of anchoring.